Loom control



Aug. 5, 1958 Filed. April 8, 1954 B. B. PURDY ETAL LOOM CONTROL 3 Sheets-Sheet 1 "INVENTORS MTW warm/1M4 AT TORNEY Aug. 5, 1958 U DY AL 2,845,958

LOOM CONTROL Filed April 8. 1954 5 Sheets-Sheet 2 BY Ma fm AT TORNEY 5. B. PURDY ETAL Aug. 5, 1958 LOOM CONTROL Filed April 8, 1954 5 Sheets-Sheet 3 INVETORS ATTORNEY United States Patent LOOM CONTROL Bruce B. Purdy and Adrian T. Godschalx, Appleton, Wis.

Application April 8, 1954, Serial No. 421,817

12 Claims. (Cl. 139-353) This invention relates to an electrical control that may be employed to govern the operation of a mechanical apparatus such as a loom and it more specifically resides in a low current responsive circuit having a control-voltage source connected to an element of a current valve to control the flow of current therethrough and with a detecting element and a conductor that is brought into electrically conducting engagement with the detecting ele-v ment upon occurrence of a condition in the apparatus that is to be detected, wherein the detecting element and conductor are electrically connected between the current valve and the control voltage source to change the voltage applied to the element of the valve to allow current to fiow therethrough for actuating a control device responsive to such current flow.

It is desirable to detect broken warp thread ends or unduly slack warp threads being advanced toward the heddles of a loom, in order to timely shut down the loom and make necessary repairs to the defective warp thread before proceeding with the weaving operation. Similarly, it is desirable to detect an excessive rise in the surface of the woven cloth before it is wound upon a finished cloth roll in order to shut down the loom operation and remove the rise which might otherwise become an injurious wrinkle if wound into the roll.

For the detection of broken warp ends and dropped warp threads it has heretofore been customary to employ so-called drops. A drop is supported upon each warp thread and upon the occurrence of a break in the warp or a slackening of the warp the drop will fall. In the fallen position the drop bridges a pair of conductors to complete a circuit that energizes a relay to effect a shut down of the loom. If a low voltage circuit is employed it is necessary to provide conductors of suificient size to carry the considerable current required for operation of the relay. On the other hand, if a high voltage circuit be employed a shock hazard is presented to the loom operator, and if the operator inadvertently contacts the high voltage conductors that are to be bridged by the drops his reaction to the shock hazard may be injurious to either himself or the work, or both.

The rapidity of response of relays operated by currents passing through drops has been of an order such that a weft may be passed through the shed and woven into the cloth by a beat subsequent to the detection of a fault, or the heddles may often pass through a change to incorporate the weft in the cloth. In the instance of weaving wire strands for cloth of highly uniform texture of loose warp causes an immediate ripple in the cloth if a subsequent beat or heddle change occurs, which ripple may seldom be removed with satisfaction. A slow response detecting circuit, such as heretofore had with drop circuits is therefore not satisfactory. Instead, an extremely rapid shut down of the loom upon detection of a defect in the Warp is required for the weaving of wire.

In the specific form of the present invention that is set forth in the description that forms a part hereof a sensitive control circuit is: employed that responds to a small current flow in a low voltage circuit utilizing detecting conductors disposed on the loom in positionto be contacted by a warp or other item to which the circuit is to be responsive. The detecting conductors form a part of a control grid circuit for a tube, the plate circuit of which actuates a control relay that causes immediate, shut down of the loom. By engaging a detecting conductor with a displaced warp, the grid voltage source is shunted with a limited current from this source being conducted through the detecting conductor and the warp. The grid bias then falls to allow the tube to conduct for the operation of a relatively high voltage control relay requiring greater power demands than the detecting conductor or warp may conduct, and which has very rapid response characteristics.

In the use of the invention drops may be, eliminated and electrically conductive strands that are to be, or have been, woven then provide a part of the detecting circuit. Usually such strands are inadequate conductors, their cross section area being too small to conduct any substantial currents. The low current required to actuate the apparatus of the present invention isof such small order, however, that the strands may conduct the same. without possibility of excessive heating, tarnishing or electrical erosion.

It is an object of this invention to provide a control circuit that will respond to a low order of current flow through low voltage conductors, thereby permitting fine conductive strands to be utilized as conductors in the control of the circuit.

It is another object of this invention to provide a circuit with a quick response to the detection of a condition in an apparatus to be controlled to operate a control relay with a minimum of time delay after occurrence of the condition detected.

It is another object of this invention to provide a control circuit for detecting the displacement of a warp thread through physical contact of a conductive warp with a detecting conductor and to draw a current flow through both the warp and the conductor.

It is another object of this invention to eliminate the need for a drop in the detection of slack or brokenwarp threads being fed to the heddles of a loom.

It is another object of this invention to provide a con?- trol circuit for detecting conditions in a loom in which detecting conductors for the circuit may be disposed open.- ly on the loom without presenting a shock hazard to the operator.

It is another object of this invention to provide a control circuit having a control tube that rapidly responds to a condition in the grid circuit through the provision of a grid discharge path of a negligible time constant.

These and other objects and advantages of this invention will appear in the description to follow. In the description reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration and not of limitation a specific form in which this invention may be embodied.

In the drawings:

Fig. 1 is a side view in elevation with parts broken away and in section of a l-oom in which this invention is embodied.

Fig. 2 is a fragmentary plan view of a detecting wire that passes beneath the warp threads and forms a part. of the loom shown in Fig. 1.

Fig. 3 is a fragmentary plan view of a detecting wire placed above finished cloth that has been woven and is to be wound upon the cloth roll of the loom.

Fig. 4 is a fragmentary plan view of another detecting wire that passes beneath the warp threads of the loom.

Fig. is a fragmentary plan view of an array of detecting wires stretched directly above the warp threads of the loom,

' Fig. 6 is a fragmentary side view in elevation of a portion of the loom shown in Fig. 1,

Fig. 7 is a fragmentary front view in elevation of the loom viewed through plane 7-7 shown in Fig. 6, and

Fig. 8 is a wiring diagram of a control circuit network employed in the control of the loom. Referring now to the drawings and more specifically to Fig. 1, there is shown a loom 1 that is particularly adapted for the weaving of wire cloth. The loom 1 has an upwardly extending right side frame 2 and a similar left side frame 3 disposed at the opposite, or left, end parts of which can be seen in Fig. l where the frame 2 has been broken away. Extending between the side frames 2, 3 at the front of the loom 1 is a breast beam 4 and disposed beneath and slightly to the rear of the breast beam 4 is a rotatably mounted cloth roll 5 upon which is wound finished cloth that has been formed through the weaving operation of the loom. At the rear of the loom 1 is a rotatably mounted warp roll 6 that is wound with a supply of warp threads 7 that are drawn forwardly from the roll 6 to a pair of heddles 8, and hence through the reed 9 of the lay 10. The warp threads 7 pass from the reed 9 to a beat line 11, from which point there extends a section of woven cloth 12 that passes about the breast beam 4 to the cloth roll 5 where it is conveniently wound.

The lay is formed with a vertically extending right side arm 13, a fragmentary portion of which is shown in Fig. 1, that is pivotally mounted at the upper end upon the side frame 2, as at 14. Similarly, a left side arm 15 is pivotally mounted upon the left side frame 3. Between the lower ends of the side arms 13, 15 there extends a horizontal lay cap 16 and a lay bottom 17 is disposed beneath the cap 16. The reed 9 is mounted between the lay cap 16 and the lay bottom 17. The lay bottom 17 is connected to one end of a piston rod 18 operated by a lay retracting cylinder 19. By alternately venting and charging the cylinder 19, through and by means not fully shown, the lay 10 may be retracted from and swung toward the beat line 11.

To pay out the warp threads 7 from the warp roll 6 a large gear wheel 20 is mounted on the shaft of the roll 6 at the outer side of the frame 2 and a worm 21 that is keyed on a shaft 22 is disposed in mesh with the gear wheel 20. A bevel gear 23 is disposed on the lower end of the shaft 22 and in driving mesh with the gear 23 is a second bevel gear 24. The bevel gear 24 is rotated, by means not fully shown, at a rate to pay out the warp threads 7 from the roll 6 as required for the particular mesh of cloth being woven.

To take up the woven cloth 12 on the roll 5 a second large gear Wheel 25 is keyed to the shaft of the roll 5. A worm 26 in mesh with the gear wheel 25 is keyed to a shaft 27 that is turned at one end through a set of bevel gears 28 and 29. The bevel gear 29, similarly as the gear 24, is rotated by means not fully shown to take up the woven cloth 12 at a desired rate. Synchronizing means, also not fully shown but which is well known in the art, coordinates the paying out of warp threads 7 from the warp roll 6 and the take-up of the woven cloth 12 on the cloth roll 5 to keep the warp threads 7 from unduly slackening or being overstressed. There is also provided supplementary tensioning means for the warp threads 7 and finished cloth 12. A bell crank lever 30 is pivoted between its ends at a point 31 to the right side frame 2. The upper end of the lever 30 mounts a roller 32 that bears against a circular plate 33 pinned to the shaft 27. The lower curved end of the lever 30 terminates in a small upwardly facing platform 34. Pivoted to the side frame 2 of the loom 1 at a point 35 directly in front of the small platform 34 of the lever 30 is a weight lever 36. The weight lever 36 extends rearwardly and mounts 4. a weight 37 at its after end. A roller 38 that bears upon the upper face of the platform 34 is also mounted on the weight lever 36 and the downward thrust of the weight 37 and lever 36 causes the bell crank lever 30 to pivot clockwise to retain the roller 32 in bearing engagement with the circular plate 33 on the shaft 27. The shaft 27 is thus urged rearwardly and the worm 26 bears against the teeth of the gear wheel 25 to urge the gear wheel 25 clockwise to place the unwound woven cloth 12 .and the warp threads 7 under tension. A similar tensioning apparatus is also mounted on the left side of the loom 1.

As is shown in Figs. 6 and 7 a bracket 39 is mounted upon the right side frame 2 at a point slightly to the front of the weight 37. Extending sidewardly from the top of the bracket 39 is a pivotally mounted arm 40 that normally assumes a horizontal position, from which it cannot descend, and from which it may be swung upwardly. Extending beneath the arm 40 is a second arm 41 pivoted to the lower end of the bracket 39. The lower arm 41 is blocked from swinging above the horizontal position, but may be swung below the horizontal. A tension spring 42 connected between the arms 40, 41 retains each in the horizontal, as shown.

The weight lever 36 normally extends between the arms 40, 41 and is closely spaced from both the underface of the arm 40 and the upper face of the arm 41. An upper electrically conductive detecting probe 43 in the form of a wire strand is extended across the underface of the arm 40 in a position to be contacted by the weight lever 36 in the event the lever 36 is raised. A second lower electrical conductive detecting probe 44 in the form of a wire strand is extended across the upper face of the arm 41 in a position to be engaged by the weight lever 36 in the event the lever 36 tilts downwardly. To insulate the probes 43, 44 from the frame of the loom 1 the arms 40, 41 are formed of a suitable insulating material and the weight lever 36, being formed of a con ducting metal, grounds the. probes 43, 44 upon making contact therewith.

As shown in Fig. 6, the probes 43, 44 each extend to a connector plug 45 mounted on a bracket 46 secured to the side frame 2. The plug 45 connects the probes 43, 44 together and joins them to the conductor of a shielded cable 47, which cable is in turn connected as hereinafter described. A similar set of probes 43', 44' are mounted on the left hand end of the loom 1 and are schematically represented in Fig. 8. A cable 47 joins with the probes 43, 44' similarly .as the cable 47 is joined with the probes 43, 44.

Referring now to Fig. 2, there is shown an end portion of a bracket 48 that is mounted on the left side frame 3 in a position as shown in Fig. 1. A second bracket 49 is mounted upon the right side frame 2 in a position corresponding to that of the bracket 48 and stretched between the brackets 48, 49 is a detecting wire 50 disposed beneath the Warp threads 7. The right end of the detecting wire 50 is secured in the base of a connector plug 51 for connection with a shielded cable 52. The opposite end of the detecting wire 50 is connected to an insulating block 53, and to retain the detecting wire 50 in a stretched state the block 53 is joined to the bracket 48 through a tension spring 54 and an eye bolt 55.

Referring now to Fig. 3, there is shown the end portion of a bracket 56 attached to the right side frame 2 in a position parallel to the woven cloth 12 about to be wound upon the roll 5, as shown in Fig. 1, and the end of a second bracket 57 attached to the left side frame 3. The brackets 56 and 57 are aligned so that a detecting wire 58 may be supported slightly above the cloth 12. The wire 58 is in the form of a closed loop, each end of the loop being held by a triangular insulator 59, and a plurality of tubular insulating sheaths 60 encircle and are spaced along the length of the wire 58. To hold the wire 58 with the sheaths hearing against the cloth 12 the right hand insulator 59 is secured to the bracket 56 and the left hand insulator 59 is secured to the bracket 57 through a tension spring 61 and a bolt 62. The detect wire 58 is connected at the right hand end through a connector plug 63, mounted on the right hand insulator 59, to a shielded cable 64 and as shown in Fig. 8 the shielded conductor of the cable 64 is connected in turn with the shielded conductor of the cable 52.

In Fig. 4 there is shown a single strand of detecting wire 65 that is stretched directly beneath the warp threads 7 in a position at the rear of the loom, as shown in Fig. l. The left hand end of the detect wire 65 is attached to an insulator 66, which in turn is supported by a tension spring 67 and an eye bolt 68 that is attached to a bracket 69 mounted upon the left side frame 3. The left end of the detect wire 65 is also connected to one end of a connector plug 70 that is joined to the shielded cable 47. The right hand end of the detect wire 65 is connected-through a connector plug 71 mounted on a bracket 72 to a shielded cable 73 that is joined at its opposite end with the cable 64, as shown in Fig. 8. The

detecting wire 65 is also joined through a lead 74 and a plug 75 to the cable 47, and through a lead 76 and a plug 77 to a shielded cable 78.

Referring now to Fig. 5, there is shown a set of four detecting wires 79, 80, S1 and 82 which extend parallel to one another between an insulating block 83 at the left side of the loom 1 and a second insulating block 84 at the right sideof the loom. The detecting wires 79--32 are mounted directly above a pair of lease rods 136 that extend along the front of that portion of the roll 6 upon which the supply of warp threads 7 is wound. The warp threads 7 alternately pass over and under the rods 136, as shown, and the detecting wires 79, are disposed over the forward rod 136, with the detecting wires 31, 82 disposed over the rear rod 136. Each wire 7982 has a plurality of spaced insulating sheaths 85 that ride upon the warp threads 7 to elevate the wires 79-82 from contacting engagement with those warps 7 that are correctly paid out from the roll 6 in normal fashion. To mount the detecting wires 7982 in this position the insulation block 83 is mounted through a tension spring 86 and an eye bolt 87 to a bracket 83 that is secured to the left side frame 3, and the insulation block 84 is mounted through a tension spring 89 and an eye bolt 90 to a bracket 91 that is attached to the right side frame 2. The detecting wires 7982 are attached to one another at the right hand ends by a jumper 92 and the lead 82 is connected through a suitable plug 93 mounted on the insulating block 84 to the shielded cable 78.

In Fig. 8 the detecting wire assemblies that have been described are schematically shown connected to one another and each detecting wire or probe is joined by the connections to an end of a lead 94 that is joined at its opposite end in a grid circuit of a tube 95 to be hereinafter described. An input transformer 96 provides a potential source for plate and grid voltages for the tube 95. The secondary winding 97 of the transformer 96 is attached to a pair of output leads 98 and 99. A pair of resistors 100 and 101, connected together by a lead 137, that act as a voltage divider network are joined between the ends of the leads 98. 99. A heating element 102 for the tube 95 is connected at one side to the lead 99 and at the other side to tap 103 in the transformer secondary winding 97. The cathode 104 of the tube 95 is connected through a lead 105 to the lead 99. A screen grid 106 is connected to the plate 107 of the tube 95, both the plate 107 and screen 106 are in turn joined through a lead 108 to one side of a coi 109 of a control relay 110. The opposite end of the coil 109 is connected through a lead 111, a resistor 112 and a .6 rectifier 113 to the lead 98. The lead 111 is connected through a lead 114 to a capacitor 115 and hence through a lead 116 to the lead 99.

The relay 110 has a set of normally open contacts 117 that are connected at one side through a lead 118 to the plate 107 and the lead 108. The opposite side of the contacts 117 is connected through a lead 119 to a normally closed push button 120, and hence through a lead 121 to the lead 99. A second set of normally closed relay contacts 122 are shown connected in a portion of a control circuit for an electro-magnetically operated clutch 123 that connects and disconnects the output shaft 124 of a drive motor 125 with a shaft 126 that is in driving relation with elements of the loom 1. One side .of the contacts 122 are joined through a lead 127 to one side of the clutch 123. The opposite side of the contacts 122 are joined to a lead 128, and the opposite side of the clutch 123 is joined to a lead 129. The leads 128 and 129 are in turn connected to a power source and other switching control for the clutch 123, which is not shown.

A grid 130 of the tube 95 is connected through a lead 131 to one end of a resistor 132. The opposite end of the resistor 132 is connected to the lead 94 and also to one end of a resistor 133. The opposite end of the resistor 133 is connected through a rectifier 134 to the common connection between the resistors 100, 101, and is also connected through a condenser 135 to the lead 99. The lead 99 is grounded by connection to the loom frame, and the warp threads 7, woven cloth 12 and weight levers 36 also being electrically joined to the loom frame are likewise at the same ground potential.

With the transformer 96 connected to a source of alternating current the resistors 100, 101 will act as voltage dividers, with the voltage across each being proportional to the respective resistance values. The capacitor 135 will be charged through the circuit comprising the resistor 100 and the rectifier 134. The rectifier is disposed so that a negative charge will be placed upon the tube grid 130 with respect to the cathode 104, and the tube 95 is then cut-off to prohibit the flow of plate current. The capacitor 135 may be selected so that it will charge in a fraction of a cycle to insure that no plate current flows upon initial charge of the capacitor, and since the tube grid draws no appreciable current the capacitor charging network will cease to deliver current as soon as the capacitor 135 has become charged. In the event that the lead 94 should be grounded by a contacting engagement of a detecting wire with a warp thread 7 or cloth 12, or 'by an engagement of a detecting probe with a weight lever 36, then the potential difference between the grid 130 and cathode 104 will fall to zero value. This change in grid bias will be nearly instantaneous since the time constant of the circuit between grid and cathode that drains the grid of its charge is very small, the only capacitance in this circuit being the inter-electrode capacitance of the grid and cathode. The inductance is negligible. The tube 95 will now conduct to energize the relay coil 109 through the circuit comprising the lead 98 connected to one end of the secondary winding 97, the rectifier 113, the resistor 112, the relay coil 109, the lead 108, the tube 95, the lead 105 and the lead 99 connected to the opposite side of the secondary winding 97. Contacts 117 close to provide a self-holding circuit for the relay 110, in which the tube 95 is shunted through the lead 118, the contacts 117, the lead 119, the normally closed push button 120, the lead 121 and a portion of the lead 99. The contacts 122 will open and the circuit for the electromagnetic clutch 123 will be opened to disengage the clutch and stop the rotation of the shaft 126. The operation of the loom 1 is thus brought to a halt. The condition of the loom that caused an operation of the circuit network to halt the loom may now be investigated and corrected. The lead 94 will then no longer be grounded, and to ready the clutch circuit for subsequent operation the push button 120 is depressed to deenergize the relay coil 109.

Upon a grounding of the lead 94 the current drain that flows from the capacitor 135 through the lead 94 and the particular detecting wire or probe engaged by a grounded warp 7, section of cloth 12 or lever 36 may be kept at minute values. For example, the resistors 100 and 101 may be selected to provide a 20 volt drop across the resistor 100. The capacitor 135, which is of small capacity to ensure nearly complete charge in less than a cycle, will then be charged to a like potential, which is sufficient to cut oil flow of plate current. Now, upon a contact of the detecting wire 65 by a warp thread 7 the current that will flow through the thread 7, the wire 65, and lead 94 will depend upon the value of the resistor 133. A value of 220,000 ohms may be selected for the resistor 133 and initial current will thus be below "a tenth of a milliarnpere. This current will further decrease as the R. M. S. value of the voltage appearing across the capacitor 135 falls with the initial discharge.

The minute current flow occuring to actuate the tube 95, and hence the relay 110, permits the use of the warp threads 7 and woven cloth 12 as portions of the detecting circuit. Further, the voltages impressed upon the Warp threads 7 and woven cloth 12 will be of a low order that excludes possibility of injurious sparking at the point of contact with one of the detecting wires 50, 58, 65, 79-82. By isolating the circuit, of which the threads 7 and cloth 12 are a part, from the highly inductive circuit of the relay 109 and by retaining the inductance of the thread and cloth circuit negligible the transient self-induced voltages incurred upon grounding the lead 94 will not rise to a value to cause an electrical erosion of the cloth or threads, or otherwise damage the same. Possible injury to the threads is thus eliminated and voltages present will not present a shock hazard to the operator. A shock hazard might cause inattention upon the part of the operator and damage may be inflicted to the work upon occurrence of a surprise move in response to a shock. The invention further provides for the use of a high voltage low current relay in the plate circuit of the tube 95, that has a rapid response, thereby causing a shut down of the loom with a minimum time delay after detection of a fault.

The detecting wires 50 and 65 are disposed to be contacted by slack warps or fallen broken warp ends. Such conditions should be timely corrected before a loose warp is intermeshed with adjacent warps by a heddle change, or 'before a beat or heddle change causes a ripple in the cloth. Similarly the detecting wire 58 is disposed to be contacted by unwanted rises in the finished cloth 12, which should be relieved before being wound upon the roll 5, and the array of detecting leads 7982 are disposed to be engaged by a warp rising above the normal path between the roll 6 and the heddles 8, as may occur for example in some instances of slackness of a warp. A further mode of detection of an unwanted condition in the loom is the positioning of detecting probes 43, 44, 43' and 44 above and below weight levers 36, to detect a shift in weight lever position that is indicative of incorrect tension in the warps 7 and cloth 12. The control circuit network of the invention thus has versatile use, by reason of the low current flow through low voltage detecting leads that causes actuation of the apparatus.

We claim:

1. In a low current responsive control circuit for a loom the combination comprising an electrical valve having a control grid, a plate, and a cathode; a plate circuit for said valve including a source of plate voltage and current responsive controlling means actuated upon the flow of plate current; an alternating current source to provide a grid voltage; a rectifier; a capacitor connected in series relation with said rectifier to said current source and joined through connections with the valve across said cathode and said control grid; an electrically conductive thread on the loom at an electrical potential substantially the same as one connection between the valve and the V capacitor; and a detecting lead joined at one end to another connection between the valve and capacitor, said lead being in closely spaced relation to the thread on the loom whereby a contact between said detecting lead and thread closes a circuit shunting said capacitor to alter the grid 'bias and affect the plate conducting characteristic of the valve.

2. In a low current responsive control circuit for a loom the combination comprising an electrical valve having a control grid, a plate and a cathode; a plate circuit for said valve including a source of plate voltage and current responsive controlling means actuated upon the fiow of plate current; contact means operable in response to actuation of said controlling means; driving means for said loom including a prime mover and an electromagnetic control operable for placing and removing said prime mover in and from driving relation to the loom; an energizing circuit for said electromagnetic control including said contact means whereby actuation of said controlling means causes said electromagnetic control to remove said prime mover from driving relation to said loom; an alternating current source to provide a grid voltage; a rectifier; a capacitor connected in series relation with said rectifier to said current source and joined through connections with the valve across said cathode and said control grid; a conductive thread on the loom at an electrical potential substantially the same as one connection between the valve and the capacitor; and a detecting lead joined at one end to another connection between the valve and rectifier, said lead being in closely spaced relation to the thread on the loom whereby a contact between said detecting lead and thread closes a circuit shunting said capacitor to alter the grid bias and affect the plate conducting characteristic of the valve.

3. In a low current responsive control circuit for a loom adapted to weave electrically conductive thread the combination comprising an electrical valve having a control grid, a plate, and a cathode; a plate circuit for said valve including a source of plate voltage and current responsive controlling means actuated upon the flow of plate current; an alternating current source for a supply of control grid bias voltage; a rectifier; a capacitor connected through said rectifier to said alternating current source; a current limiting resistance; connections including said resistance joining said capacitor to the control grid and cathode of said valve, connections at one side of the capacitor being disposed at a potential level like that of the thread of the loom; and a detecting lead joined at one end to said connections at the side of the capacitor opposite that at a potential level like that of loom threads extending in closely spaced relation to the loom threads whereby a contact between said detecting lead and a thread closes a circuit shunting said rectifier through said current limiting resistance, said lead and the thread to cause a change in grid bias voltage that affects the flow of current in said plate circuit.

4. In a low current responsive circuit for the control of an apparatus the combination comprising a control tube having a plate, control grid and cathode; an alternating current plate voltage source; a relay having a coil excited in response to plate current flow and a set of selfholding contacts connected at one side to said coil that are actuated upon energization of the coil; a rectifier; a plate circuit for said tube joining said rectifier to said relay coil at the side opposite said self-holding contacts and placing the rectifier and coil in series relation with said plate voltage source whereby said relay is excited upon said tube becoming conductive for a flow of plate current; a grid bias source; tube shunting connections joining the side of said self-holding contacts opposite that connected to said coil to the plate voltage source for placing the rectifier and coil across the plate voltage source upon closure Olf the self-holding contacts a grid bias circuit for said tube joining the grid bias source to the grid and cathode of said tube to place a voltage upon the tube grid to cut off the flow of plate current in the tube thereby rendering said relay to be operably inactive;

a conductive detecting lead; a conductive element forming a part of the apparatus to be controlled movable upon occurrence of an unwanted condition in the apparatus into electrical contacting relation with said detecting lead; and connections joining said detecting lead and said conductive element in said grid bias circuit shunting said control grid and cathode upon occurrence of a contacting relation of said detecting lead and said conductive element to draw current from the grid bias source through the lead and element and drop the value of bias voltage on said control grid to alter the flow of plate current.

5. In a low current responsive circuit for the control of an apparatus the combination comprising a source of alternating current; a control tube having a plate, grid and cathode; a relay having a coil and contacts operable in response thereto; a first rectifier; a plate circuit connecting said plate and cathode to said alternating current source through said coil and said first rectifier; a voltage dividing resistance network energized by said alternating current source; a bias capacitor; a second rectifier; a charging circuit for said capacitor joining said capacitor through said second rectifier across a portion of the voltage dividing network; connections joining said capacitor across the grid and cathode of said tube to place a grid bias voltage on the tube to reduce flow of plate current; a detecting lead; and an element movable to indicate a condition in the apparatus disposed to contact said lead upon occurrence of the condition, said lead and said ele ment being electrically connected to the cathode and grid of said tube to form a shunt path across said capacitor upon contact of the lead and element thereby discharging the capacitor and afiecting a change in grid bias voltage.

6. In a low current responsive circuit for the control of an apparatus the combination of an electrical valve having a plate, cathode and control grid; a plate voltage source; a control element; a plate circuit for said valve including said plate voltage source and said control element; an alternating current source for a supply of control grid voltage; a rectifier; a capacitor connected through said rectifier to said alternating current source; connec tions joining one side of said capacitor to said control grid and the opposite side of said capacitor to said cathode; a first conductive detection element electrically connected to one side of said capacitor; and a second conductive detection element electrically connected to the opposite side of said capacitor, said detection elements being engageable with one another upon occurrence of an event to be detected whereby upon engagement said rectifier is shunted to cause a change in grid bias voltage that affects the flow of current in said plate circuit.

7. In a low current responsive circuit for the control of an apparatus the combination of an electrical valve having a plate, cathode and control grid; a plate voltage source; a control element; a plate circuit for said valve including said plate voltage source and said control element; an alternating current source for a supply of control grid voltage; a rectifier; a capacitor connected through said rectifier to said alternating current source; a current limiting resistance; a first conductive detection element; a second conductive detection element, said detection elements being engageable to make contact with one another upon occurrence of an event to be detected; and connection-s joining said capacitor across the cathode and control grid of said valve with one of said detection elements being joined to one side of the capacitor and the other of said detection elements being joined through said current limiting resistance to the opposite side of said capacitor, whereby upon a contact of said detecting elements said rectifier is shunted through said current limiting resistance and said detecting elements to cause a change in grid bias voltage that affects the flow of current in said plate circuit.

8. A low current responsive circuit in accordance with claim 7 in which said control element constitutes a relay having a coil in said plate circuit and self-holding 10 contacts operable thereby; and in which there is a sec ond rectifier, and connections joining said second rectifier, relay coil and self-holding contacts in series across said plate voltage source whereby upon closure of said selfholding contacts said relay coil will remain energized.

9. In a control for a loom the combination comprising an electrical valve having a control grid, a plate, and a cathode; a plate circuit for said valve including a source of plate voltage and current responsive controlling means actuated upon the fiow of plate current; an alternating current source to provide a grid voltage; a rectifier; a capacitor connected in series relation with said rectifier to said current source and joined through connections with the valve across said cathode and said control grid;

" tension means for applying tension to warp threads upon the loom including a lever the position of which is indicative of thread tension and which lever moves in one direction upon occurrence of excessive tension and in the opposite direction upon occurrence of insufiicient tension; and a detecting contact means operable by said lever upon movement of the lever in either direction indicative of excessive or insufiicient tension; said contact means being connected across said connections with the cathode and control grid of said valve whereby operation of contact means shunts said capacitor to alter the grid bias and affect the plate conducting characteristic of the valve.

10. In a control for a loom the combination comprising an electrical valve having a control grid, a plate, and a cathode; a plate circuit for said valve including a source of plate voltage and current responsive controlling means actuated upon the flow of plate current; an alterating current source to provide a grid voltage; a rectifier; a capacitor connected in series relation with said rectifier to said current source and joined through connections with the valve across said cathode and said control grid; a lease rod; warp threads extending across said lease rod and at an electrical potential substantially the same as one connection between said capacitor and said valve; and a detecting lead transverse of the warp threads spaced from and aligned with a surface of the lease rod across which the warp threads pass joined to the other connection between said capacitor and the valve whereby a contact between a warp thread and said detecting lead shunts said capacitor to alter the grid bias and aifect the plate conducting characteristic of the valve.

11. In a control circuit the combination comprising a current valve having a plate, cathode and control grid; an alternating current plate voltage source; a relay having a coil excited in response to plate current fiow and selfholding contacts responsive to the coil; 21 rectifier; a plate circuit for said current valve joining the rectifier, coil and plate in series with the plate voltage source, and connecting the self-holding contacts in shunt with the plate and cathode of the valve to provide an energizing circuit for the coil through the rectifier, the coil itself and the selfholding contacts; a control grid circuit adapted to place a potential on the control grid sufiicient to reduce plate current below a value that causes said coil to actuate the self-holding contacts; and detecting elements in the grid circuit adapted to change the potential on the control grid to permit a plate current that causes the coil to actuate said self-holding contacts.

12. In a control circuit the combination comprising a current valve having a plate, cathode and control grid; an inductive control element; a plate circuit for the valve including said control element; an alternating current source; a rectifier; a capacitor connected through said rectifier to said current source and being joined across the cathode and grid of said valve; a pair of detection elements joined to the grid and cathode; and current limiting resistance joining, and being the sole circuit component disposed between, the end of the capacitor joined to the grid and the detection element also joined to the grid.

References Cited in the file of this patent UNITED STATES PATENTS Mummert Sept. 27, 1927 5 Pelikan June 20, 1939 Sepavich et a1. Feb. 17, 1948 Sepavich .et a1 Feb. 17, 1948 Matweeff Nov. 9, 1948 Vrooman Sept. 20, 1949 Matthias May 10, 1950 Metcalf -N0v. 28, 1950 Cochran'- Aug. 26, 1952 Fisher May 26, 1953 Lebocey Feb. 23, 1954 FOREIGN PATENTS Germany Oct. 17, 1931, 

